Device for osteosynthesis

ABSTRACT

A bone plate system includes (a) Bone Plate having a bottom surface for contacting bone, an upper surface and at least one through hole extending from the bottom surface to the upper surface, the through hole having a central axis and a cross-section that extends orthogonally to the central axis and is one of at least partially polygonal, at least partially prismatic, and at least partially elliptical; (b) Bushing within the through hole, Bushing including a central bore designed to receive a bone fixation element, a cross-section of Bushing orthogonal to the longitudinal axis of Bushing is shaped substantially the same as the cross-section of the through hole so that Bushing is secured against rotation about its longitudinal axis; and (c) at least one Bone Fixation Element having a portion for anchoring within bone, Bone Fixation Element configured and dimensioned for insertion into the central bore of Bushing.

RELATED APPLICATIONS

The present application is a Continuation application of U.S. patentapplication Ser. No. 12/698,433 filed Feb. 2, 2010 now U.S. Pat. No.8,216,283 which is a Continuation application of U.S. patent applicationSer. No. 10/877,096 filed Jun. 24, 2004 now U.S. Pat. No. 7,682,379which is a Continuation application of PCT Patent Application Serial No.PCT/CH2001/000740 filed Dec. 24, 2001. The disclosures of theseapplications are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a device for osteosynthesis, and moreparticularly, to a fixation device, such as a bone plate, having apolyaxial bushing and screw assembly for securing such a device to bone.

BACKGROUND OF THE INVENTION

Assemblies of the present type serve for screwing together elements suchas pedicle screws or pedicle hooks in a polyaxial, rigid manner, and areused in particular in the area of the spinal column. However, theseassemblies may also be employed for plating in general. Additionalfields of application include use in combination with external fixatorsand intervertebral implants.

A device of this type is shown in U.S. Pat. No. 6,235,033, in which ascrew head and the bore of the bone plate are held together by anangularly adjustable, annular bushing which is compressible andexpansible by means of a slot so as to achieve an improved fastening ofthe screw in the plate. This known device, however, suffers from thedisadvantage that the bushing used is of circular shape so that it mayrotate together with the screw as the screw is screwed in, thuspreventing it from becoming locked within the plate. The bushing mayeven turn around completely within the plate hole, so that the wrongside thereof faces upward (the inner cone tapering in the wrongdirection). The present invention is intended to provide a remedy forthis undesirable movement of the bushing relative to the bone plate.

It is accordingly an object of the present invention to provide a devicefor osteosynthesis in which the bone screws are polyaxially movable andlockable in an angularly stable manner relative to the bone platewithout the need for any additional mechanical elements.

It should be emphasized that the discussion of the state of the art asset out above is merely intended to illustrate the background of theinvention and does not mean that at the moment of filing the presentapplication, or its priority application, the cited state of the art wasactually published or otherwise publicly known.

SUMMARY OF THE INVENTION

According to the invention, this object is achieved by means of a devicefor osteosynthesis comprising a fixation element having a through holedesigned to receive a multiaxially pivotal bushing for a bone screw, thethrough hole having a central axis and a non-circular cross-sectionextending orthogonally to the central axis; and a bushing insertable insaid through hole, the bushing including a central bore designed toreceive a bone screw, the bore having a longitudinal axis, and aperipheral outside surface configured and dimensioned to be in contactwith at least a portion of the interior surface of the through hole. Thebushing is configured and dimensioned to be radially compressible andradially expansible, and a cross section of the bushing extendingorthogonally to the longitudinal axis of the bushing is shapedsubstantially the same as the cross section of the through hole suchthat when the bushing is inserted in the through hole, it is securedagainst rotation relative to its longitudinal axis while remainingpivotally adjustable relative to the fixation element.

As used herein, the term “non-circular” refers to any cross sectiondeviating from an exactly circular shape, and refers in particular, butis not limited to, prismatic and elliptical cross sections.

One advantage achieved by the device of the present invention consistsin the fact that the bushing can no longer turn about its own axis whilethe bone screw is screwed in. The turning of said bushing would in factentail that no relative movement between the bushing and the screw wouldtake place, and that the bushing would, therefore, not be expanded.Consequently, a locking of the screw would not be possible. A furtheradvantage consists in the fact that, unlike the device disclosed in U.S.Pat. No. 6,235,033, an additional locking screw is unnecessary.

In one particular embodiment, the cross section of the through holeformed in the osteosynthetic device, which, in a preferred embodimentincludes a bone plate, is polygonal, preferably hexagonal, so that saidthrough hole has the form of a prism, preferably a hexagonal prism. Inthe case of the hexagonal embodiment, the bone screw may besimultaneously moved in three planes within the hexagonal through hole,making it possible to adjust and fix the screw at any desired angle.Said angle is only limited by the plate thickness and by the abutment ofthe bushing on the reduced cross section. It is of course also possibleto use bone plates having a plurality of through holes.

In a further embodiment, the diameter of the central bore of the bushingtapers in one direction and the bore is preferably shaped in the form ofa cone. This configuration permits the bushing to be spread apart bymeans of a corresponding counter cone. However, the bore formed in thebushing may also be realised in a circular cylindrical shape.

Preferably, the bore of the bushing is provided with an internal screwthread. This permits a locking of the bushing.

Extending orthogonally to the central axis, the cross section of thethrough hole formed in the osteosynthetic device, which is preferablyrealised as a bone plate, may also be of elliptical shape.

In a specific embodiment, the cross section of the through hole consistsof two incomplete semicircles connected to one another by means ofnon-circular lines. In this case, the bushing is provided with twoprotrusions formed on its outer surface which may be inserted into thegrooves formed in the through hole by the non-circular lines.

In order to be radially compressible and radially expansible, thebushing may be provided with a continuous slot preferably extendingparallel to the longitudinal axis of the bushing. In an alternativeembodiment, the bushing may also have a plurality of non-continuousslots preferably extending parallel to the longitudinal axis.

The surface of the bushing, preferably in the area of its peripheral,outer surface, is suitably roughened, e.g. by means of grit blasting.The through hole formed in the bone plate may correspondingly beroughened, e.g. by means of grit blasting. However, the surface of thebushing, preferably in the area of its peripheral, outside face, mayalso be provided with a macrostructured portion, e.g. in the form ofperipheral ridges. The through hole may then be correspondingly providedwith a macrostructured portion, e.g. in the form of peripheral ridges.The advantage of this configuration lies in the positive engagementbetween the bushing and the bone plate which is thus achievable.

In another specific embodiment, the through hole formed in theosteosynthetic device, which, in a preferred embodiment includes a boneplate, tapers towards the bottom surface and preferably also towards thetop surface, thus resulting in reduced cross sections which prevent thebushing from falling out or from being pressed out. Suitably, thereduced cross section of the through hole and the compressibility of thebushing are selected adequately so that it is still possible tointroduce the compressed bushing into the through hole.

The form of the peripheral outside face of the bushing is suitablyconvex, and preferably cylindrical.

Preferably, the osteosynthetic device—at least in the area of itsthrough hole—and the bushing—at least in the area of its peripheraloutside face—consist of different materials, preferably of materialsdiffering from each other in hardness. The bushing may, for example,consist of a biocompatible plastic material and the osteosyntheticdevice (e.g. a bone plate) of a biocompatible metal. However, thebushing may also be made of metal and the device of a plastic material,preferably a reinforced plastic material. The different materials causea plastic deformation of the surfaces and thus lead to a positiveengagement.

The height of the bushing measured in the direction of its longitudinalaxis should be inferior to the height of the through hole formed in thebone plate as measured in the direction of its central axis. The heightof the bushing may be between 40 and 85 percent of the height of thethrough hole. In one specific embodiment, the height of the bushing maybe between 45 and 65 percent of the height of the through hole.

The bone screws to be introduced into the bushing preferably have aconical screw head which is provided with an external screw thread. Theadvantage of this configuration is that the spreading and the locking ofthe bushing may thus be realised in a single step.

In the following, the invention and improvements of the invention willbe illustrated in greater detail with reference to the partiallydiagrammatic representations of several embodiments. All the embodimentsrelate to an osteosynthetic device including a bone plate. Analogousapplications for pedicle screws, pedicle hooks, external fixators, orintervertebral implants are also possible and within the scope of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1 is a perspective view of a fixation element according to apreferred embodiment of the present invention, wherein the fixationelement is a bone plate;

FIG. 2 is a cross section of the bone plate according to FIG. 1 with abushing introduced therein;

FIG. 3 is a perspective view of a bushing according to a preferredembodiment of the present invention;

FIG. 4 is a horizontal cross section of the bushing shown in FIG. 3;

FIG. 5 is a perspective view of a bushing according to another preferredembodiment of present invention;

FIG. 6 is a horizontal cross section of another variation of a boneplate according to the present invention;

FIG. 7 is a perspective view of a bushing according to another preferredembodiment of the present invention, which mates with the bone plateaccording to FIG. 6; and

FIG. 8 is a longitudinal section of a bone screw to be used with adevice for osteosynthesis according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The device for osteosynthesis represented in FIGS. 1 to 4 consists of abone plate 1 including a bottom surface 2 designed to bear against thebone, a top surface 3, and a through hole 4 connecting the bottomsurface 2 with the top surface 3, designed to receive a multiaxiallyadjustable bushing 10 for a bone screw 20 (FIG. 8), the through hole 4having a central axis 5. The bushing 10 (FIG. 3) insertable into thethrough hole 4 includes a central bore 11 designed to receive the bonescrew 20 (FIG. 8), the bore 11 having a longitudinal axis 12, as well asa peripheral outside face 17 designed to be in contact with the throughhole 4.

The bushing 10 has a continuous slot 13 so as to be radiallycompressible and radially expansible. The through hole 4 of the boneplate 1 is provided, toward the bottom surface 2 and toward the topsurface 3 thereof, with a reduced cross section 9 so as to prevent thebushing 10 from falling out or from being pressed out. Suitably, thereduced cross-section 9 of the through hole 4 and the compressibility ofthe bushing 10 are selected adequately so that it is still possible tointroduce the compressed bushing 10 into the through hole 4.

As shown in FIG. 3, the surface of the bushing 10 is provided, in thearea of its peripheral, outside face, with a macrostructured portion inthe form of peripheral ridges 18. Correspondingly, the through hole 4 ofthe bone plate 1 is provided with a macrostructured portion in the formof peripheral ridges 19 (FIG. 2).

As shown in FIG. 4, the cross section 6 of the through hole 4 extendingorthogonally to the central axis 5 is shaped in an approximatelyhexagonal, i.e. non-circular form. The cross section 16 of the bushing10 extending orthogonally to the longitudinal axis 12 has a formcorresponding substantially to that of the cross section 6 of thethrough hole 4 of the bone plate 1, so that the bushing 10 which isplaced in the through hole 4 is rotationally stable relative to itslongitudinal axis 12, while remaining adjustable within the through hole4 as to its angular orientation relative to the bone plate 1.

As shown in FIG. 2, the diameter of the bore 11 tapers in the directionof the bottom surface 2 of the bone plate 1, so that the bore 11 has aconical shape. In addition, the bore 11 is provided with an internalscrew thread 15.

FIG. 5 shows another embodiment of the bushing 10 which comprises aplurality of non-continuous slots 14 extending parallel to thelongitudinal axis 12. This permits the bushing 10 to be radiallycompressible and radially expansible without having a continuous slot.

FIGS. 6 and 7 show another embodiment of the bushing 10 and of thecorresponding bone plate 1 in which the cross section 6 of the throughhole 4 is defined by two incomplete semicircles 7 connected to eachother by means of two non-circular lines 8. Corresponding to this, thebushing represented in FIG. 7 is shaped in the form of a ring theperipheral outside face 17 of which is spherical and which is providedwith two diametrically opposed semicircular protrusions 26. The twoprotrusions 26 are received by the grooves formed by the non-circularlines 8 within the through hole 4 of the bone plate 1, which is equallyspherical. When inserted into the bone plate, the bushing 10 isrotatable both about the two protrusions 26 and orthogonally to thisaxis of rotation, so that adjusting movements are possible in alldirections apart from a movement in the plane of the plate (cardanjoint).

The bushing 10 may receive the bone screw 20 represented in FIG. 8. Thebone screw 20 has a threaded shaft 21 permitting it to be anchoredwithin the bone, a screw axis 23, and a screw head 22 for insertion intothe central bore 11 of the bushing 10, which corresponds substantiallyto the shape of the bore 11. The cross section of the screw head 22,which extends orthogonally to the screw axis 23, has a tapered portionproximal to the screw shaft 21, thus forming a cone. The screw head 22is provided with an external screw thread 24 which corresponds to theinternal screw thread 15 of the bushing 10. In addition, the screw head22 is provided with a hexagon socket 15 for receiving an Allen key (notshown in the drawing).

In the following, the clinical utilization of the device forosteosynthesis will shortly be described.

The bushing 10 of the device comes preassembled in the bone plate 1 orin the jaw. It therefore does not need to be inserted by the surgeon.The bone plate with the preassembled bushings is applied to the bone.This may be done either before or after the reduction of the differentbone fragments or vertebral bodies. There are three possible scenariosfor placing the bone screws: a) drilling, tapping, screwing; b)drilling, screwing (using self-tapping screws); or c) screwing (usingself-drilling and self-tapping screws).

It is also possible to use aiming devices or drill bushings. It is ofcourse not suitable to use fixed aiming devices, as this would typicallynegate the advantage of an angularly adjustable screw, but such anaiming device may nonetheless make sense in cases in which a limitationof the range of adjustment is desirable. Drill bushings are needed incases in which no self-drilling screws are used and a hole must bedrilled prior to inserting the screw. In such cases the drill bushingserves to prevent soft-tissue injury.

There are basically two possible ways of placing a plurality of bonescrews:

A) if bone reduction is done prior to the application of the plate, thescrews may immediately be fastened; and

B) in cases in which bone reduction is done after the application of theplate, the screws are first turned in only so far as to fix the plate onthe bone; after that, the final bone reduction or correction takes placeand the screws are subsequently turned in a few more angular degrees soas to become locked within the plate.

While the present invention has been described with reference to thepreferred embodiments, those skilled in the art will recognize thatnumerous variations and modifications may be made without departing fromthe scope of the present invention. Accordingly, it should be clearlyunderstood that the embodiments of the invention described above are notintended as limitations on the scope of the invention, which is definedonly by the following claims.

What is claimed is:
 1. A bone plate system, comprising: a bone platehaving a bottom surface for contacting bone, an upper surface and atleast one through hole extending from the bottom surface to the uppersurface, the through hole having a central axis and a cross section thatextends orthogonally to the central axis and is one of at leastpartially polygonal, at least partially prismatic, and at leastpartially elliptical; a bushing within the through hole, the bushingincluding a central bore designed to receive a bone fixation element,wherein a cross section of the bushing orthogonal to the longitudinalaxis of the bushing is shaped substantially the same as the crosssection of the through hole so that the bushing is secured againstrotation about its longitudinal axis; and at least one bone fixationelement having a portion for anchoring within the bone, the at least onebone fixation element being configured and dimensioned for insertioninto the central bore of the bushing.
 2. The system of claim 1, whereinthe bushing has at least one continuous slot.
 3. The system of claim 1,wherein the bushing has a height measured in a direction of itslongitudinal axis, and the through hole of the bone plate has a heightmeasured in a direction of its central axis, and the height of thebushing is less than the height of the through hole.
 4. The system ofclaim 1, wherein the bore of the bushing has a cylindrical shape.
 5. Abone plate system, comprising: a bone plate having a lower surface forcontacting bone, an upper surface and at least one through holeextending from the lower surface to the upper surface, the through holehaving a central axis defining a vertical centerline and a cross-sectionextending orthogonally to the vertical centerline defined by twoincomplete semicircles connected to each other by at least twonon-circular cut outs forming grooves in the bone plate; at least onebushing insertable in the through hole, the bushing comprising: a topsurface; a bottom surface; a longitudinal axis substantiallyperpendicular to the top and bottom surfaces of the bushing; a centralbore designed to receive a bone screw; and a peripheral outside facehaving at least two outwardly extending protrusions defining an axis ofrotation of the bushing extending through the protrusions; and at leastone bone screw having a threaded shaft for anchoring within the bone, alongitudinal screw axis, and a screw head configured and dimensioned forinsertion into the central bore of the bushing, wherein the bushing isconfigured and dimensioned to be radially compressible and radiallyexpansible; and wherein a cross section of the bushing orthogonal to thelongitudinal axis of the bushing is shaped substantially the same as thecross section of the through hole such that when the bushing is insertedinto the through hole, the bushing is pivotable about the axis ofrotation defined by the protrusions.
 6. The system of claim 5, whereinthe bushing has at least one continuous slot.
 7. The system of claim 6,wherein the slot extends parallel to the longitudinal axis of thebushing from the top surface of the bushing to the bottom surface of thebushing.
 8. The system of claim 5, wherein the screw head of the screwis conically tapered.
 9. The system of claim 8, wherein the screw headof the screw is at least partially threaded.
 10. The system of claim 5,wherein the bushing has a height measured in the direction of itslongitudinal axis from the top surface to the bottom surface, and thethrough hole of the bone plate has a height measured in the direction ofits central axis from the upper surface to the lower surface, and theheight of the bushing is less than the height of the through hole. 11.The system of claim 5, wherein the two outwardly extending protrusionsare configured and adapted to be insertable into the grooves in the boneplate.
 12. The system of claim 5, wherein the bushing has a second axisof rotation orthogonal to the axis of rotation defined by theprotrusions.
 13. The system of claim 12, wherein the bushing ispivotable about the axis of rotation defined by the protrusions and thesecond axis of rotation when the bushing is inserted into the throughhole.
 14. The system of claim 5, further comprising a plurality ofthrough holes and a plurality of bushings inserted into the plurality ofthrough holes.